Research Helps Lay Out Theory for Metamaterials That Act as an Analog Computer

A new study by researchers at the University of Pennsylvania, The University of Texas at Austin and University of Sannio in Italy shows that metamaterials can be designed to do "photonic calculus" by working like an analog computer.

"Thanks to recent advances in nanotechnology, today we are able to control light propagation through a material in unprecedented ways and realize material functionalities that would have been unthinkable only a few years ago," said author Andrea Alù, associate professor and David and Doris Lybarger Endowed Faculty Fellow in engineering at UT Austin's Cockrell School of Engineering. "In this paper, we set the stage to have metamaterials realize a broad set of mathematical operations for us on-the-fly, as light propagates through them."

Francesco Monticone, a graduate researcher and Ph.D. student in the Cockrell School's Department of Electrical and Computer Engineering, also collaborated on the study.

By swapping analog computers' mechanical gears and electrical circuits for optical materials that operate on light waves, it may once again be the computers' time to shine, but this time at the micro- and nanoscale.

"Compared to digital computers, analog computers were bulky, power hungry and slow," said senior author Nader Engheta, the H. Nedwill Ramsey Professor of Electrical and Systems Engineering in Penn's School of Engineering and Applied Science. "But by applying the concepts behind them to optical metamaterials, one day we might be able to make them at micro- and nanoscale sizes, and operate them at nearly the speed of light using little power."

Metamaterials are composites of natural materials but are designed in such a way that they manipulate electromagnetic waves in ways that are more than the simple sum of their parts. Multiple manipulations can be combined or performed in sequence, allowing metamaterial researchers to change the shape of waves in complex ways.

A light wave, when described in terms of space and time, has a profile in space that can be thought of as a curve on a Cartesian plane. The researchers' theoretical material can perform a specific mathematical operation on that wave's profile, such as finding its first or second derivative, as the light wave passes through the material.

Essentially, shining a light wave on one side of such a material would result in that wave profile's derivative exiting the other side. Metamaterials capable of other calculus operations, such as integration and convolution, could also be produced.

Viewing and manipulating this type of light wave "profile" is an everyday occurrence for applications such as image processing, though it is typically done after the light wave has been converted to electronic signals in the form of digital information. The researchers' proposed computational metamaterials could almost instantly perform such operations on the original wave, such as the light coming in through the lens of a camera, without conversion to electronic signals.